It is known to cover wood window and door frames with plastic coverings. As an example, U.S. Pat. No. 3,340,665 provides a protective coating for window frames which is separately formed from a rigid plastic material and then fitted over a separate wooden frame. If desired, both interior and exterior surfaces of the wood frame can be covered with the plastic channel members and then joined together via heat fusion or mechanical means.
As noted hereinabove, it is also possible to fabricate frame members and related components out of fiberglass and other thermosetting plastics in order to provide durability. In order to fabricate fiberglass profiles, it is known to employ apparatus for the continuous pultrusion of articles having a predetermined cross section. Nevertheless, one of the shortcomings of pultrusion is the limited fabrication ability to continuously produce fine details and sharp corners. Because fiberglass can weather, from an aesthetic standpoint it has become desirable to provide a surface coating of a thermoplastic polymer as a protectant and to enhance the appearance.
As will be explained in greater detail hereinbelow, the present invention provides a method whereby various profiles of thermosetting plastics are given a thermoplastic coating which allows much greater adaption or end use in that a wide range of different cross sections or geometries can be manufactured The method employs a step of crosshead extrusion which heretofore has not been conducted satisfactorily, if at all.
At least one process is known for applying a thermoplastic resin to plastic pipes via crosshead extrusion. The process is described in U.S. Pat. No. 4,515,737 and begins with the extrusion of a non-reinforced plastic in a continuous, cylindrical profile. Next, longitudinal strands of fiber roving are resin impregnated with a thermosetting plastic, wrapped around the pipe and cured. Finally the surface of the pipe is given a surface coating of a thermoplastic, via crosshead extrusion.
This process is limited to the manufacture of a relatively simple plastic pipe having only convex surfaces, not concave or undercut profiles. Also, the process requires a filament winding step to provide the desired transverse strength and finally, there is no provision for integrally bonding the thermosetting polymer to the thermoplastic pipe.